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authorManfred Spraul <manfred@colorfullife.com>2014-12-13 03:58:14 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-13 23:42:52 +0300
commite843e7d2c88b7db107a86bd2c7145dc715c058f4 (patch)
tree01557305cc1446467c9e70ba287f9b0360c9e1ce
parent2e094abfd1f29a08a60523b42d4508281b8dee0e (diff)
downloadlinux-e843e7d2c88b7db107a86bd2c7145dc715c058f4.tar.xz
ipc/sem.c: increase SEMMSL, SEMMNI, SEMOPM
a) SysV can be abused to allocate locked kernel memory. For most systems, a small limit doesn't make sense, see the discussion with regards to SHMMAX. Therefore: Increase the sysv sem limits so that all known applications will work with these defaults. b) With regards to the maximum supported: Some of the specified hard limits are not correct anymore, therefore the patch updates the documentation. - SEMMNI must stay below IPCMNI, which is 32768. As for SHMMAX: Stay a bit below this limit. - SEMMSL was limited to 8k, to ensure that the kmalloc for the kernel array was limited to 16 kB (order=2) This doesn't apply anymore: - the allocation size isn't sizeof(short)*nsems anymore. - ipc_alloc falls back to vmalloc - SEMOPM should stay below 1000, to limit the kmalloc in semtimedop() to an order=1 allocation. Therefore: Leave it at 500 (order=0 allocation). Note: If an administrator must limit the memory allocations, then he can set the values as necessary. Or he can disable sysv entirely (as e.g. done by Android). Signed-off-by: Manfred Spraul <manfred@colorfullife.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Acked-by: Rafael Aquini <aquini@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/uapi/linux/sem.h18
1 files changed, 15 insertions, 3 deletions
diff --git a/include/uapi/linux/sem.h b/include/uapi/linux/sem.h
index 541fce03b50c..dd73b908b2f3 100644
--- a/include/uapi/linux/sem.h
+++ b/include/uapi/linux/sem.h
@@ -63,10 +63,22 @@ struct seminfo {
int semaem;
};
-#define SEMMNI 128 /* <= IPCMNI max # of semaphore identifiers */
-#define SEMMSL 250 /* <= 8 000 max num of semaphores per id */
+/*
+ * SEMMNI, SEMMSL and SEMMNS are default values which can be
+ * modified by sysctl.
+ * The values has been chosen to be larger than necessary for any
+ * known configuration.
+ *
+ * SEMOPM should not be increased beyond 1000, otherwise there is the
+ * risk that semop()/semtimedop() fails due to kernel memory fragmentation when
+ * allocating the sop array.
+ */
+
+
+#define SEMMNI 32000 /* <= IPCMNI max # of semaphore identifiers */
+#define SEMMSL 32000 /* <= INT_MAX max num of semaphores per id */
#define SEMMNS (SEMMNI*SEMMSL) /* <= INT_MAX max # of semaphores in system */
-#define SEMOPM 32 /* <= 1 000 max num of ops per semop call */
+#define SEMOPM 500 /* <= 1 000 max num of ops per semop call */
#define SEMVMX 32767 /* <= 32767 semaphore maximum value */
#define SEMAEM SEMVMX /* adjust on exit max value */